Polyols are very well known to those skilled in the art due to their utility as reactants for the preparation of a variety of polymeric or resin compositions. Typical reactions include curing or crosslinking reactions with isocyanate or polyisocyanate materials having at least two isocyanate groups per mole, melamines or formaldehyde compounds.
One class of polyols includes polyester polyols or the hydroxy terminated polyesters. These are generally prepared by an esterification reaction of a diol or mixtures of diols and triols with a dicarboxylic acid or anhydride. Examples of such suitable diols and triols are ethylene glycol, propylene glycol, 1,3 propane diol, 1,4 butane diol, neopentyl glycol, trimethylol propane and the like. Examples of such dicarboxylic acids and anhydrides are phthalic acid, phthalic anhydride, isophthalic acid, maleic acid, maleic anhydride, succinic acid, adipic acid and the like. These polyester polyols, however, are generally high viscosity compounds which, when mixed with a curing or crosslinking agent, have to be diluted or dissolved in relatively large amounts of a suitable solvent in order to provide low viscosity, easy to apply coating compositions.
Because a large amount of solvent is required to reduce the viscosity of these polyols, they are not suitable for the formulation of high solids coatings. Moreover, due to the presence of the solvent, these polyols cannot be used in compounds for potting or molding applications.
A second class of polyols is the acrylic polyols. These are prepared by the copolymerization of a hydroxy acrylate or methacrylate with acrylate and/or methacrylate esters or styrene. Examples of suitable monomers are hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, methyl acrylates, ethyl acrylate, butyl acrylates, 2-ethylhexyl acrylate, methyl methacrylate, butyl methacrylate and the like.
These hydroxy-containing acrylic polymers, like the polyester polyols, are high viscosity compounds which, when mixed with the desired curing or crosslinking agent, also require large amounts of solvent to provide low viscosity, easy to apply coating compositions. Again, due to the presence of a large amount of solvent, these polyols are not suitable for the high solids coatings, or for potting and molding applications.
A third class of polyols comprises polyether polyols. These are prepared by the homopolymerization and copolymerization of ethylene oxide and propylene oxide. Although some of the polyols in this class have acceptable viscosity, particularly those with low molecular weights, they are not suitable for high solids coating applications because of their relatively poor physical properties. Specifically, these deficient properties include poor light stability, poor weathering properties, and poor solvent and water resistance.
Cyclopentadiene has been copolymerized with drying and semidrying oils by a process described in U.S. Pat. No. 2,390,530 to Gerhart for the purpose of providing inexpensive, solid resin compositions which are suitable as "gums" or resins for ultimate use in paints and varnishes. These oils include linseed oil, soybean oil, perilla oil, oiticica oil, tung oil, cotton oil, palm oil, and sunflower oil. U.S. Pat. No. 2,392,140, also to Gerhart, describes a process for the polymerization of cyclopentadiene either alone or conjointly with an equimolar ratio of a glyceride oil or an ethylenic compound such as indene, coumarone, methyl methacrylate, styrene, or maleic anhydride. The resulting resins, at least while hot, are liquid and can be admixed with additional drying oils, thinners, and the like to obtain a resin paint or varnish of desired viscosity and color.
While the above-described resins are useful for certain paint and varnish compositions, they do not contain any hydroxyl groups which can be reacted with a curing or crosslinking agent such as a polyisocyanates, melamines, or formaldehyde compounds to form high solids resin coatings.
One family of resin compositions which contains the requisite hydroxyl groups is the alkyd resins. These alkyd resins are produced as products of an esterification reaction involving a polyhydric alcohol, i.e., a polyol such as glycerol, sorbital, ethylene glycol or pentaerythritol, and a polybasic acid.
The resultant polyester resins, of which the alkyds are one type, may then be modified with monobasic fatty acids, most of which are derived from natural drying and nondrying oils, such as linseed oil, soybean oil and castor oil, to form resin compositions having acceptable properties for certain applications.
Castor oil is a triglyceride ester of ricinoleic acid and contains approximately 3 hydroxyl groups per molecule. It is, therefore, a polyester polyol which can be reacted with isocyanates, polyisocyanate, melamine, formaldehyde or polybasic acid compounds. These castor oil compositions, however, have relatively poor mechanical properties and solvent resistance.